The invention relates to so-called propellant grains, namely monolithic, unitary propellant structures of a nongranular nature, and more particularly, to a process for producing such grains.
As used herein, the terms grain or grains accordingly refer to such unitary structures or what may be termed macrostructures or unitary grains rather to granular materials as typically of powders and granular propellants in the form of minute particles.
Presently, unitary grains of a propellant or other ignitable material or mixture are prepared individually in molds of various sizes and shapes. In the molding of a propellant or other ignitable material or mixture, it is known that the problem of interfaces and voids in the resulting grain acutely affects the burn pattern of the grain as well as its ability to withstand limited amounts shearing and stress.
Because present industry practice relies typically upon molding each grain individually, there is a great deal of labor involved. Moreover, present industry practice also contributes to both the presence and frequency of interfaces and voids in each grain and also results in a low degree of uniformity from grain-to-grain and a considerable amount of waste.
Molding of unitary cartridge charges dates to at least as early as Lamm U.S. Pat. No. 435,842 issued in 1890 which proposed molding cylindrical charges of what then was termed explosive material but was in probability a fusible propellant composition. A more recent example of the patented art is U.S. Pat. No. 3,353,438 issued to Scanlon and Quinlan for a device for molding propellant cylinders for use in caseless ammunition in which a casing received propellant composition and cylindrical member was insertable into the cavity receiving the composition for forming a bore thereof. The latter method is but one known method of tube casting of grains. Tube casting has the known difficulty of permitting voids or more subtle discontinuities to be introduced into the limited amount of composition placed in the tubular mold cavity.
Similarly it has been known to use split molds for casting of grains. Split molds also may permit voids or discontinuities but also may leave mold flash or sprue remnants. A grain formed by such mold casting technique may accordingly require objectionable, time-consuming lathe turning under precise, care-intensive control regimes to remove unwanted projections or to achieve a final cylindrical dimension. Moreover, such casting methodologies offer only limited ultimate grain geometries or surface topologies.
Stacking of layers of propellant is also well known, as taught by Maxim U.S. Pat. No. 778,788, but stacking of propellant or combustible mixtures, with attendant disadvantages and limitations, is not suitable to certain propellant devices in which is it is desired to have the advantage of using grains of unitary nature.
Although the term propellant grain is used in the present disclosure, it will be understood to comprehend ignitable or combustible grains not necessarily used as a propellant per se but having other uses when the grain is ignited such as, without limitation, for controlled release of substances or as a carrier for substances including gaseous propellant component or reaction mixture discharge. E.g., such a grain may serve a gas generator function.